The present invention relates to a system for effecting annealing treatments, particularly for annealing embrittled reactor vessels.
During the normal operation of a nuclear reactor, the reactor vessel, which is normally made of steel and which houses a core containing nuclear fuel, is exposed to intense radiation. Experience has shown that this radiation causes changes in the fine grain structure of the steel walls of the vessel. These structural changes make the walls brittle, a problem commonly referred to as reactor vessel embrittlement. Embrittlement reduces the flexibility of the vessel wall and increases the susceptibility of the vessel wall to fracturing, particularly if subjected to sudden stresses, such as due to operating transient events and pressurized thermal shock events.
Because of this embrittlement phenomenon, the United States Nuclear Regulatory Commission requires that a reactor vessel be removed from service when embrittlement reaches a predetermined stage, thus ending the useful life of this portion of the nuclear power plant. Replacement of such a vessel is extremely expensive because the vessel is built into and is a part of the reactor containment building, thereby making replacement economically impractical.
In order to deal with this problem, it has been proposed to subject such a vessel to annealing in place in order to restore the ductility and toughness of the metal constituting the reactor vessel.
Since it is not feasible to remove a reactor vessel from the reactor installation and transport it to an annealing facility, a practical annealing system must be capable of treating the vessel in place. However, because such an annealing treatment would be required only once, or possibly a few times, during the useful life of a vessel, it is equally unfeasible to provide annealing equipment at each reactor location, given the complexity and high cost of such annealing equipment. Finally, the transport of equipment required to perform an annealing operation by conventional transport procedures, and subsequent set up of such equipment at a reactor location would add significantly, and perhaps prohibitively, to the total cost of an annealing operation.